Re: [Qemu-devel] How to create PCH to support those existing driver

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Aug 18, 2014 at 05:01:25PM +0800, Chen, Tiejun wrote:
> On 2014/8/18 16:21, Michael S. Tsirkin wrote:
> >On Mon, Aug 18, 2014 at 11:06:29AM +0800, Chen, Tiejun wrote:
> >>On 2014/8/17 18:32, Michael S. Tsirkin wrote:
> >>>On Fri, Aug 15, 2014 at 09:58:40AM +0800, Chen, Tiejun wrote:
> >>>>Michael and Paolo,
> >>>
> >>>Please re-post discussion on list. These off list ones are just
> >>>wasting time since they invariably have to be repeated on list again.
> >>
> >>Okay, now just reissue this discussion to all related guys. And do you think
> >>we need to discuss in public, qemu and xen mail list?
> >
> >Absolutely.
> 
> Now -CC qemu, xen and intel-gfx.
> 
> If I'm missing someone important please tell me as well.
> 
> >
> >>>
> >>>>After I created that new machine specific to IGD passthrough, xenigd, now I
> >>>>will step next to register the PCH.
> >>>>
> >>>>IIRC, our complete solution should be as follows:
> >>>>
> >>>>#1 create a new machine based on piix, xenigd
> >>>>
> >>>>This is done with Michael help.
> >>>>
> >>>>#2 register ISA bridge
> >>>>
> >>>>1> Its still fixed at 1f.0.
> >>>>2> ISA bridge's vendor_id/device_id should be emulated but then
> >>>>	
> >>>>	subsystem_vendor_id = PCI_VENDOR_ID_XEN;
> >>>>	subsystem_device_id = ISA Bridge's real device id
> >>>>
> >>>>This mean we need to change driver to walk with this way.
> >>>>For example, in
> >>>>case of Linux native driver,
> >>>>
> >>>>intel_detect_pch()
> >>>>{
> >>>>	...
> >>>>	if (pch->subsystem_vendor == PCI_VENDOR_ID_XEN)
> >>>>		id = pch->subsystem_device & INTEL_PCH_DEVICE_ID_MASK;
> >>>>
> >>>>Then driver can get that real device id by 'subsystem_device', right?
> >>>>
> >>>>This is fine now but how to support those existing drivers which are just
> >>
> >>Here correct one point, we don't need to care about supporting the legacy
> >>driver since the legacy driver still should work qemu-traditional. So we
> >>just make sure the existing driver with this subsystem_id way can support
> >>those existing and legacy platform.
> >>
> >>Now this is clear to me.
> >>
> >>>>dependent on checking real vendor_id/device_id directly,
> >>>>
> >>>>	if (pch->vendor == PCI_VENDOR_ID_INTEL) {
> >>>>		unsigned short id = pch->device & INTEL_PCH_DEVICE_ID_MASK
> >>>>
> >>>>Maybe I'm missing something, please hint me.
> >>>>
> >>>>Thanks
> >>>>Tiejun
> >>>
> >>>The subsystem id was just one idea.
> >>
> >>But from that email thread, "RH / Intel Virtualization Engineering Meeting -
> >>Minutes 7/10", I didn't see other idea we should prefer currently.
> >>
> >>>What was finally agreed for future drivers is that guests will get all
> >>>information they need from the video card, this ID hack was needed only
> >>>for very old legacy devices.
> >>>http://article.gmane.org/gmane.comp.freedesktop.xorg.drivers.intel/42258
> >>>So this is for newer guests, they will work without need
> >>>for hacks, like any other device.
> >>>
> >>
> >>Actually we had a meeting to discuss our future solution, but seems you were
> >>on vacation at that moment :)
> >>
> >>In that meeting we had an agreement between us and some upstream guys.
> >>
> >>We will have such a PCI capability structure in this PCI device to represent
> >>all information in the future. This make sens to Intel as well.
> >>
> >>Maybe Allen or Paolo known more details.
> >>
> >>But obviously this a long-term solution, so currently we will work with this
> >>subsystem_id way temporarily. And this way is accepted by those guys in the
> >>meeting.
> >
> >
> >I don't see the point really. If you are modifying the driver,
> 
> Yes, we need to modify something in the driver.
> 
> >why not modify it to its final form.
> 
> What's your final form?

Avoid poking at other devices besides the passed through card.
Get everything from BAR and other registers of the card.

> As I track that email thread, seems the follows is just a way you guys
> achieve a better agreement.
> 
> "
> > why not set the subsys vid to the RH/Quamranet/Virtio VID, so it's
> > obvious for the use-match?
> 
> That's exactly the suggestion.  Though upstream they might be using the
> XenSource id since the patches were for Xen.
> 
> Paolo
> "
> Or I'm missing something?
> 
> Thanks
> Tiejun


I thought the point of this work is to make existing
linux/windows drivers work. Is it or isn't it?

Wrt changing drivers, change them to behave sanely, like all other
drivers, and avoid poking at the chipset.
http://article.gmane.org/gmane.comp.freedesktop.xorg.drivers.intel/42258
Seems to suggest one way to do this.
Can what is suggested there work for existing devices?


> >
> >>>
> >>>For existing drivers: Vendor ID is intel anyway.
> >>
> >>Yes.
> >>
> >>>For device ID, override it through a property
> >>>or something. But I think poking at the real host from
> >>>qemu is a mistake though, host is not
> >>>protected by iommu.
> >>>Two possible suggestions were to reverse-detect
> >>>id of the device from the card that is assigned,
> >>
> >>I guess you're saying pci_get_device(vendor/devices_ids), right?
> >>
> >>>or just make it a user property, and move the smarts
> >>>to management.
> >>
> >>Sorry could you elaborate this way in detail?
> >>
> >>Thanks
> >>Tiejun
> >
> >
> >Will do but let's do it on the mailing list.
> >